What should be the included angle of a twist drill when working with soft metals?

The included angle of a twist drill is important when considering the material being worked on. For soft metals, an included angle of 90 degrees is optimal. This angle strikes a balance between providing enough cutting edge for effective penetration into the metal while also preventing excessive wear and heat buildup during the drilling process.

A 90-degree included angle ensures that the cutting edges remain sharp and efficient, allowing for smoother drilling and better chip removal. This also helps to reduce the risk of deformation or damage to the drill bit itself when it encounters softer materials, which can be more susceptible to issues like galling or tool wear.

In contrast, angles that are either too sharp or too blunt may not perform well with soft metals. For example, smaller angles can lead to a point that is too fragile and may chip or break easily, while larger angles might not engage with the material effectively, leading to poor cutting performance. Therefore, a 90-degree twist drill is particularly well-suited for drilling into soft metals, making it the preferred choice.